A secondary battery refers to a battery capable of being charged and discharged, unlike a primary battery which is not possible to be charged. As an example, a low capacity battery in which one battery cell is packaged in a pack form has been mainly used in small portable electronic devices such as a portable terminal, a note book, a computer, and a camcorder. As another example, a large capacity secondary battery in which a plurality of battery cells are connected in series or in parallel has been used in devices requiring high power, for example, power supply for driving motor of an electric vehicle, and the like.
The secondary battery is possible to be manufactured in various shapes. As representative examples, the secondary battery is manufactured in a pouch-shape, a cylindrical shape, and a prismatic shape, and the like. Among them, the pouch type secondary battery is relatively free in view of a shape, and has a light weight, to be widely used in portable electronic devices requiring slimness and lightweight in recent years.
FIG. 1 is a perspective view schematically showing a general pouch type lithium secondary battery.
Referring to FIG. 1, the general pouch type lithium secondary battery (1) is provided with a pouch packing material (hereinafter, referred to as a “pouch” 10) that is sealed along an edge. The pouch 10 includes a thin metal film and insulating films attached on both surfaces thereof to be freely bendable.
In addition, electrode laminates (not shown) are embedded in the pouch 10, and in order to embed the electrode laminates in the pouch 10, a predetermined space part for accommodating the electrode laminates may be formed in an inner portion of the pouch 10.
Meanwhile, a pair of electrode tabs 20 and 30 protrude toward an outer portion of the pouch 10, and these electrode tabs 20 and 30 may be electrically connected to the electrode laminates embedded in the pouch 10.
However, in the case of the pouch type lithium secondary battery, a passage with an outer portion is completely blocked at the end stage of manufacturing the battery, in order to prevent introduction of water and air.
However, this blocking structure may be a factor that prevents discharge of gas generated by deterioration in view of characteristics of the lithium secondary battery.
That is, when gas generated in the inner portion of the pouch is not smoothly discharged, but increased in a predetermined amount or more, appearance deformation of the pouch may be caused. Due to the deformation, internal electrode laminates are out of an initially arranged state and disorderly arranged. As a result, short-circuit may occur and even the short-circuit may become a cause of smoke or ignition.
Korean Patent Laid-Open Publication No. 10-2013-0102807 (Publication Date: Sep. 23, 2013) which is a relevant prior art discloses a lithium polymer secondary battery.